A. Field of Invention
The present invention relates generally to electronics, and more specifically to professional or commercial microphones and audio accessories.
B. Description of the Related Art
Microphones are acoustic-to-electric transducers or sensors that convert sound into electrical signals. A common microphone design uses a thin membrane which vibrates in response to sound pressure. Most microphones in use today use electromagnetic induction (dynamic microphone), capacitance change (condenser microphone), piezoelectric generation, or light modulation to produce the signal from mechanical vibration.
Condenser microphones, also known as capacitor microphones, contain a capacitor that has two plates with a voltage between them. One of the plates is known as the diaphragm and is made of a very light material. The diaphragm vibrates when struck by sound waves, changing the distance between the plates and therefore changing the capacitance and forming an electrical signal, which then needs amplification. When the plates are closer together, capacitance increases and a charge current occurs. When the plates are further apart, capacitance decreases and a discharge current occurs. A voltage must be supplied across the capacitor either by battery or external phantom power. Condenser microphones produce a high-quality audio signal and are popular in laboratory and studio recording applications. They have a greater frequency response and transient response, which is the ability to reproduce the “speed” of an instrument or voice.
The way that microphones pick up sound from different directions is known as a pickup pattern. The patterns are usually depicted as polar diagrams, a circular graph of sensitivity of a microphone from various directions. A microphone's directionality or polar pattern indicates how sensitive it is to sounds arriving at different angles about its central axis. Depending on the situation, some microphone patterns are more suitable than others. For example, an omnidirectional pattern picks up sound well from all directions and is frequently used for recording ambient and background sound. A uni-directional pattern is most sensitive to sound coming from directly in front of the microphone. This pattern is useful when sounds are coming from a specific direction. A heart-shaped pattern, known as a cardioid pattern, rejects sound coming from the back of a microphone and is progressively more sensitive to sounds as the direction approaches the front of the microphone. The cardioid pattern is favored for stage use, as they do not readily pick up sound from on stage speakers or monitors, thus preventing feedback.
Typically, the structure of the microphone defines its directivity and its polar pattern. The structural shape of the microphone capsule has been of major importance in determining the pickup pattern. For example, a capsule that is closed on one side results in an omni-directional pattern, while the cardioid pattern results from a capsule with a partially closed backside. Remote control of microphone polar patterns has previously been achieved only through special, multi-conductor cables and connects.
Therefore, what is needed is a method and apparatus for the remote control of polar patterns in continuously variable pattern microphones using standard microphone cabling.